Surface properties and graphitization of polyacrylonitrile based fiber electrodes affecting the negative half-cell reaction in vanadium redox flow batteries

Langner, Joachim; Bruns, Michael; Dixon, Ditty; Nefedov, Alexei; Wöll, Christof; Scheiba, Frieder; Ehrenberg, Helmut; Roth, Christina; Melke, Julia

doi:10.1016/j.jpowsour.2016.04.128

Cited by 86 publications

(83 citation statements)

References 49 publications

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“…The relatively large exchange current densities of the KF grades in the negative electrolyte can again be attributed to the high content of surface functional groups. This is consistent with recent studies by Langner et al., who found that the reactivity of activated PAN‐based felts towards the V 2+ /V 3+ couple increases as the temperature of graphitization decreases. Structural defects and surface oxygen groups favor the adsorption of vanadium species, thereby improving charge‐transfer kinetics.…”

Section: Resultssupporting

confidence: 93%

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

2017

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Carbon felts based on rayon and polyacrylonitrile (PAN) precursors constitute the most widespread porous electrode material for vanadium redox‐flow batteries. Since the raw materials exhibit rather poor wettability, it has become common practice to apply oxidative surface treatments prior to use in flow batteries. This study investigates the electrode‐specific effects of raw and thermally oxidized (PAN and rayon‐based) carbon felts on their electrochemical behavior at the negative and the positive electrode in all vanadium redox‐flow batteries. By means of steady‐state single cell measurements, it is verified that oxidative surface treatment has opposite effects on negative and positive redox couples and that the beneficial influence on the vanadium redox‐flow battery performance is mainly brought about by substantially improved charge‐transfer kinetics at the negative electrode. Similarly, the type of carbon precursor and the degree of graphitic character have a particular impact on the electrode behavior.

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Section: Resultssupporting

confidence: 93%

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

2017

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“…This observation is in line with several previous studies. 20,[22][23][24]35 The positive half-cell does not show any significant changes in overpotential before and after heat-treatment of the electrode materials.…”

Section: Resultsmentioning

confidence: 93%

“…21 Many recent studies focusing on both vanadium redox reactions involved in the VRB have shown that the overpotential associated with the negative half-cell dominates the voltage losses of the VRB and limits performance. [22][23][24][25] Many efforts have been successfully undertaken to improve the electrochemical activity of various carbon materials, which result in better VRB performance. However, despite these improvements, some of the modified carbon materials are not suitable for use in the VRB because of their poor operational lifespan.…”

mentioning

confidence: 99%

Performance of Different Carbon Electrode Materials: Insights into Stability and Degradation under Real Vanadium Redox Flow Battery Operating Conditions

Nibel

Taylor

Pătru

et al. 2017

J. Electrochem. Soc.

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This work focuses on the performance and stability of selected commercial carbon electrode materials before and after heat-treatment in an operating all-vanadium redox flow battery (VRB). Heat treatment results in improved cell performance for all tested materials, with SGL 39 AA carbon papers and SIGRACELL GFD4.6 EA carbon felt showing the best performance. Further investigation of these two materials by in situ reference electrode measurements reveal improvements after heat-treatment that originate mainly from the negative electrode or V 2+ /V 3+ side of the cell. Upon extended cycling, carbon felt is found to be stable. Carbon papers however, show significant performance losses originating from the negative electrode side. The potential limit during charging and the exposure to very negative potentials appears to be a critical issue at the negative electrode in the VRB. Analysis of both materials after cycling by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy reveal significant differences in their surface chemistry, structure and morphology. These differences give valuable insights into the behavior and degradation of different carbon materials used in VRBs. Redox flow batteries (RFBs) are a promising technology for efficient energy storage and grid stabilization.1,2 The all-vanadium redox flow battery (VRB), which uses vanadium ions in different oxidation states at the positive and negative electrodes, is the most advanced RFB to date.3 The electrodes are a crucial component of the VRB, as they provide the surface on which the respective electrochemical reactions occur. Thus, catalytic activity, wettability and mass transport properties of the electrodes strongly affect VRB performance. Ideal electrodes for the VRB should provide both: long term durability and stable catalytic activity. Various materials have been considered as electrodes for the use in VRBs including non-carbon based dimensionally stable anode electrodes and carbon based electrodes such as carbon felt, carbon paper, carbon nanotubes, carbon nanofibers or graphene oxides. 4 To enhance electrochemical activity and wettability of carbon based materials in VRBs, different surface modification methods have been used. Carbon electrodes have been coated with metals such as iridium, 5 doped with nitrogen 6 or decorated with nanomaterials such as graphene-nanowalls 7 or graphite carbon nanotubes. Most of these surface treatment approaches introduce functional groups, commonly oxygen onto the carbon electrode surface. This leads to increased wettability and redox activity, which is generally attributed to the increased concentration of surface-active oxygen functional groups.11 Among the various surface modifications, heattreatment is still regarded as the most common and facile approach to incorporate oxygen groups onto the surface of carbon materials. 4 In an effort to better understand the role of oxygen functional groups on electrode performance, Fink et al. studied pristine and heat-treated Rayon (a regene...

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“…A possible explanation could lie in the catalysis of the HER brought about by residual nitrogen groups. 31 Bulk and surface analysis of PAN-based carbon fibers 32,39 have shown that the oxygen groups are preferentially located on the fiber surface, whereas the bulk nitrogen content is larger than its surface fraction. This is because the oxygen groups are formed at reactive surfaces (edge planes) whereas the nitrogen content, which originates from the PAN precursor, is caused by nitrogen atoms which are incorporated into the carbon ring system (chinoline or quaternary nitrogen groups, e.g.).…”

Section: Resultsmentioning

confidence: 99%

Parasitic Hydrogen Evolution at Different Carbon Fiber Electrodes in Vanadium Redox Flow Batteries

Schweiss

Pritzl

Meiser

2016

J. Electrochem. Soc.

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Carbon fiber-based fabrics such as felts, cloths or papers are porous electrode materials that are widely used in redox flow batteries. This study investigates the effect of the carbon fiber properties on hydrogen evolution at the negative electrode, which occurs as an important side reaction in redox flow batteries employing acidic electrolytes. The lowest hydrogen evolution rate was observed at carbon fibers with a high content of graphitic domains which have been subjected to surface oxidation pre-treatment. By contrast, felt materials consisting of fibers with a largely amorphous character produce elevated amounts of hydrogen during battery charging. Differences between rayon-and polyacrylonitrile (PAN)-derived carbon fibers point toward the important role of nitrogen species. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.1281609jes] All rights reserved. Redox flow batteries are regarded as promising candidates for large-scale electrochemical storage systems for energy generated from fluctuating sources such as wind farms or photovoltaic systems.1-5 One of their widely acclaimed features is their inherent safety. Among other aspects, this is owing to the fact that the active masses consist of rather dilute, aqueous solutions of redox species (typically 1.5 to 3 molar) which are continuously circulated through an electrochemical reactor during operation. Consequently, only a small fraction of the redox species is present at any given time in the electrochemically active area, while the major part remains in electrolyte tanks, where it acts as a powerful thermal buffer.The obvious drawback of the aqueous cell chemistry is the relatively small electrochemical window, which is limited by the onset of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Since common electrolytes contain strong acids with concentrations of up to 4 moles per liter in order to provide high ionic conductivity, the electrochemical window is reduced even further.Three-dimensional porous carbon electrodes such as felts, which are commonly manufactured from rayon (cellulose) or polyacrylonitrile (PAN) precursors, are well suited for these batteries since they come at a low cost, have a large surface area and exhibit sufficiently large overpotentials against hydrogen and oxygen evolution. [6][7][8][9][10][11] In the literature they are widely referred to as 'graphite' felts as they are processed at high temperatures similar to those used in the manufacturing of synthetic graphite. The fraction of crystalline domains, however, amounts to less than 50% 10 and the crystallographic d...

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Surface properties and graphitization of polyacrylonitrile based fiber electrodes affecting the negative half-cell reaction in vanadium redox flow batteries

Cited by 86 publications

References 49 publications

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

Steady‐State Measurements of Vanadium Redox‐Flow Batteries to Study Particular Influences of Carbon Felt Properties

Performance of Different Carbon Electrode Materials: Insights into Stability and Degradation under Real Vanadium Redox Flow Battery Operating Conditions

Parasitic Hydrogen Evolution at Different Carbon Fiber Electrodes in Vanadium Redox Flow Batteries

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